1. Field of the Invention
The present invention relates to a path search method of a spread spectrum communication system and a receiver using the method, and more particularly to a path search method of a spread spectrum communication system, which is effective in miniaturization and reduction in consumption power and a receiver using the method.
2. Description of the Related Art
The receiver of the spread spectrum communication system is used in a CDMA (Code Division Multiple Access) and the like.
Generally, in the receiver of the spread spectrum communication system, a multipart occurs due to reflection and the like. For this reason, regarding the respective multipath components, the receiver of the spread spectrum communication system detects distribution (delay profile) of reception power with respect to delay time at its arrival time, and manages the delay profile data individually.
The receiver of the spread spectrum communication system comprises a plurality of finger circuits that despreads baseband signals, a rake circuit that performs rake combining of the despread signals output from the plurality of finger circuits, and a path searcher that transmits reception timing to the finger circuits.
The path searcher calculates the delay profile data from the baseband signals, and stores them to be equalized at a period of time (one frame) of, for example, 10 ms.
For this reason, the number of path search sample points, which corresponds to oversampling times of a spreading cycle in one symbol, is normally needed, and extends to 1024 in some cases. In the case of using diversity, the number of delay profile data to be stored is doubled as compared with the normal case. This results in the enlargement of the circuit scale of such as a memory that stores the delay profile data, a register, and the like.
The above-mentioned problem results from the conventional path search method. The path search means that the delay profile data are calculated to detect the peak of the calculated delay profile data. The conventional path search method is illustrated in FIG. 7. In FIG. 7, a horizontal axis indicates time and a vertical axis indicates reception power. In the conventional path search method, the delay profile data are calculated in a path search range (one window) of one symbol (t0 to t5) around a maximum peak. In this example, three peaks are detected by comparison among the delay profile data as illustrated in this figure.
In the case where a correlator is operated at one sample point per One delay profile data calculation, the correlators at all sample points are operated, so that power to be consumed is increased.
Since the number of correlators that calculate the delay profile data are related to the number of sample points of the delay profile data, the reduction in the number of sample points decreases the number of correlators, making it possible to reduce power consumption. However, in the simple reduction in the number of sample points, there is a possibility that tracking accuracy of reference reception timing at which the path search is carried out will be also reduced.